Since having a high ratio of surface area per volume, the nanostructures may exhibit more excellent characteristics compared to general materials in energy, electronic, chemical, and environmental applications. Nanostructures are classified into 0D structures to 2D structures according to the structures thereof, and particularly, 1D nanostructures have varying conductive characteristics according to the aspect ratios thereof. In particular, electrical characteristics of the 1D nanostructure are affected by own resistance of the structures and contact resistance between the structures, and the longer and thinner the 1D structure, the better the electrical conductivity. The electrical conductivity mechanism of the 1D nanostructure is based on the percolation theory. More specifically, the longer the nanostructure, the smaller the number of contacts present in series within a certain distance. In addition, the thinner the nanostructure, the greater the number of contacts present in parallel within the certain distance, and according to such serial or parallel distribution, an effect of inducing reduction of total resistance may be achieved. When classified according to aspect ratios, the 1D nanostructures may be classified into nanorods, nanowires, and nonfibers. Among these, since their own thicknesses and lengths of the nanowires are determined by a concentration of solute in a solution, there is a limitation in that aspect ratios the nanowires cannot be easily adjusted. In addition, since the own lengths of the nanowires are also at a level of 10 micrometers, the aspect ratios are not large and the nanowires show a limitation in an aspect of their own electrical conductivity.
From this background, among the 1D nanostructures, nanofibers which are produced by electrospinning may realize the highest aspect ratio. Nanofibers are important in that a solution that can solve the limitation of existing nanowires may be provided thereby. Nanofibers are produced through electrospinning. Electrospinning is a method for producing nanofibers on the basis of a solution and has a merit in that a great amount of nanostructures may be produced at a low process cost. In the electospinning, nanofibers are produced through a method in which a high voltage of several tens of KV is applied to a solution to induce electrostatic repelling force, and in this state, a syringe is pressed by means of a pump. In particular, the thicknesses of nanofibers may simply be adjusted by adjusting the voltage applied to the solution, and since the lengths thereof are also greater than 100 μm, the aspect ratios thereof are also large. In addition, characteristics of the nanofibers may be improved through the alignment of nanofibers. Basically, the solution used for electrospinning is composed of polymer matrices and a solvent for forming nanofibers. To produce nanofibers including a material such as a semiconductor, a precursors or nanoparticles should be dissolved together into an existing solution. After the electrospinning, the compositions, phases, and structures of materials included in nanofibers may be controlled through a subsequent calcination process.